In order to increase the recording density in hard drive disks, magnetic heads are being produced with an inductive write head element and a magnetoresistive effect (MR) read head element. The basic concept of magnetoresistive element is that resistance of such element changes as a function of applied magnetic field. Such elements can be produced by using an anisotropic magnetoresistive effect (AMR) element, a giant magnetoresistive effect (GMR) element such as a spin-valve MR element or a tunnel magnetoresistive effect (TMR) element to increase element sensitivity.
A magnetic head with a defective read head structure will not follow predictable resistivity changes over the range of magnetic read signals from a disk. Accordingly, it is important to qualify each magnetic head by testing the magnetic head for instabilities or noise.